Presentation on theme: "Electricity and magnetism"— Presentation transcript:
1 Electricity and magnetism CHAPTER 7Electricity and magnetism
2 Electric Charge and Forces Section 1Electric Charge and Forces
3 Electric ChargesAtoms are made of electrons moving around a nucleus (protons and neutrons).Protons have a positive charge.Neutrons have a neutral or no charge.Electrons have a negative charge.Atoms are electrically neutral in charge having equal protons and electrons.Losing an electron makes the atom positively charged.Gaining an electron makes the atom negatively charged.
4 Forces Between Charges Like charges repel and unlike charges attractDistance and amount of charge determines the force between objectsGreater distance = less forceGreater amount = greater force
5 Electric Field and Forces Objects do not have to touch to exert electric forces on each otherElectric fields surround every proton and electronElectric fields are invisible and at every point in space surrounding a charge.
6 Electrically Charging Objects Charging by contact – objects must come into direct contact with each otherElectrons are gained by one object and lost by the otherCharging by induction – rearranging electric charges due to the presence of an electric fieldOne part of the object is positively charged while another part is negatively charged
7 Conductors and Insulators Conductors hold electrons so loosely that they can move through the material easilySilver, gold, copperInsulators hold electrons so tightly that they cannot move through the material easilyPlastic, glass, rubber, wood
8 Static ChargeThe imbalance of electric charges on an object is called static charge.Occurs during charging by contactThe movement of static charge from one place to another is called electric discharge.Lightning – may occur between cloud and ground, within cloud, or between clouds
9 Electrostatic potential 30,000 volts removing sweater10,000 volts using a comb3,000 volts walking on carpet1,000 volts putting on coatLUCKY FOR US, these high volts have very low amperage.
10 Lightning Safety 30-30 rule If there is 30 seconds between thunder and lightning, seek shelter and stay away from metals.Wait 30 minutes after last lightning strike before leaving shelter.Storm clouds need not be present for lightning to strike.Grounding is providing a path to drain excess electric charges into EarthLightning rods
11 FUN FACTS 50-100 lightning bolts hit the ground every second on Earth. Lightning discharge 100 million volts of electricity, heating the air to 60,000 degrees F.Bolts can be up to 100 miles longSteel turns into a magnet if struck be lightning.
13 Electric Current The flow of electric charges Electrons in a wire moving along the wireEqual numbers of protons and electrons in wire making it electrically neutralEqual numbers of electrons entering wire and exiting the other endMeasured in amperes (A) = the amount of electrons flowing in and out of wire every second [about 6 billion billion]
14 Simple Electric Circuit Electricity is either static or currentStatic - electrons accumulate and "stand" on the surfaceCurrent - electrons must "flow" through somethingDirect current (DC) - flow in one direction (battery)Alternating current (AC) - reverses its flow many times a second (household power)Electric current will flow continually on a closed path known as an electric circuitBroken wires, opened switch, broken filament will stop current flowing
15 Flowing Electric Charges A force must be exerted on electric charges to make them flowAn electric field in the circuit will move electrons in a single directionA battery will produce an electric field when a chemical reaction in the battery occurs.Charges terminals of battery – and +Electrons flow from – to +
16 Electrical Resistance Electrons have trillions of collisions every second inside batteries changing their direction and speedThe electric field keeps the electrons flowing in the direction of the currentThe measure of how difficult it is for an electron to flow in an object is known as electric resistance.Measured using ohms (Ω)
17 Electrical Energy Transfer Electrons flowing through a circuit have kinetic energyEvery collision causes some energy to be converted into heat and lightAs the strength of the electric field increases so does the kinetic energy of the flowing electrons
18 VoltageThe measure of electrical energy transferred by an electron as it moves from one point to another in a circuitMeasured using a voltmeterBattery voltage indicates that there is more electrical energy transferred in higher voltage
19 Ohm’s Law Shows relationship between voltage, current, and resistance As voltage increases, current in the circuit increases.Increasing resistance slows down the current flowvoltage(V) = current(A) X resistance(Ω)V = IR
20 Series and Parallel Circuits Devices connected so there is only one closed path for current to follow is a series circuit.Any part of path broken, current will not flow.Devices connected so there is more than one closed path for current to follow is called a parallel circuit.If one path is broken, current will continue to flow through another path.
21 Electric Cost Companies charge by the kilowatt-hour (kWh) That is the amount of energy equal to 1kW of power continuously for 1 hourAbout ten 100-W light bulbs for 1 hour
23 Magnetic Poles Every magnet has a north and a south pole. Magnetic poles are like electric charges.Like poles repel; unlike poles attract.Forces are stronger the closer they are to each other.Magnetic fields are like electrical fields.Fields are stronger at the poles of magnets.
24 Magnetic MaterialsMetals that contain iron, nickel, cobalt and a few other rare-earth elementsObjects that do not contain the above elements are not effected by magnetic fields.
25 Magnetic DomainA group of atoms that have their magnetic poles pointing in the same direction has magnetic domain.With magnetic domains aligned in a single direction, the magnetic field is stronger.Materials become magnetized when magnets exert forces on the materials magnetic domains.
26 ElectromagnetismDiscovered in early 1800s, a wire carrying an electric current is surrounded by a magnetic fieldMagnetic fields can be made stronger by wrapping the wire around an iron core.Increasing current, increases the magnetic field.Electromagnets are temporary and can be controlled.
27 Generating Electric Current Moving a magnet through a wire loop that is part of a circuit makes an electric current flow – electromagnetic inductionGenerators convert mechanical energy to electrical energy.Power plants use steam or moving water to convert mechanical energy to electrical energy.